Various technologies make use of high energy radiation, such as X-ray and extreme ultraviolet (EUV) radiation. Because of the nature of this type of radiation, it is often difficult to control its divergence. One common optical element that is used to control the divergence of an X-ray beam is a collimator commonly called a Soller slit. Soller slits generally comprise an array of parallel, or nearly parallel, plates or blades that limit the divergence of an X-ray beam by simple blocking or absorption of divergent rays, which restrict the rays so that they only pass through an open section of the array.
Soller slit devices for collimation of X-rays and other high energy radiation have a variety of commercial applications. One such application that employs a Soller slit as an X-ray collimator is X-ray diffractometry. Some examples of elements measured by way of X-ray diffractometry include pharmaceutical pills, powder within capillaries, and powder between plates. X-ray diffractometry can make use of either transmissive or reflective measurements of incident X-rays.
X-ray diffractometry is the most widely used form of X-ray diffraction in the world. Thus, Soller slits that can be used for X-ray diffractometry are highly desirable for commercial diffractometry applications. Many devices using traditional Soller slits have already been developed for X-ray diffractometry.
Because X-ray diffractometry produces and requires measuring a weak signal, the diffracted X-ray signal is conventionally measured over a long period of time, typically several hours. Therefore, an increase in transmission efficiency of the X-ray optics (e.g., a Soller slit device) would be advantageous, as processing time could be greatly reduced due to stronger incident radiation, which in turn produces a proportionally stronger diffracted signal.
One problem generally associated with Soller slit devices used for commercial applications such as X-ray diffractometry, however, is that they generally have relatively low transmission efficiencies and large divergence angles. For example, a typical Soller slit device may have a transmission efficiency of 30% or less. Thus, well over half of the X-ray radiation incident upon the device is lost and unusable for measurements in the application in which the Soller slit is being employed. Additionally, typical divergence angles for known Soller slit devices generally range from 0.2° to 0.8°. This typical divergence angle is large, and negatively impacts the Soller slit's ability to effectively collimate x-ray radiation for commercial applications such as X-ray diffractometry.
It has been generally thought that materials of high density, such as dense metals (e.g., molybdenum or brass) were needed in Soller slits, to provide adequate absorption for the high energy divergent X-rays. As a result, the blades of Soller slits have traditionally been made out of sheets of heavy, or highly absorbing metal. Although these metal sheets can be made extremely thin, the mechanical stability of such thin sheets is not sufficient for high precision X-ray applications. For example, any curling or rumpling of the sheets, which is common with metals, will result in poor transmission through the Soller slit device, and consequently unpredictable divergence.
Consequently, metal-foil Soller slits have been made with relatively thick foils (e.g., on the order of 250 μm). These metal foil devices yield relatively low transmission efficiencies. Moreover, the transmission efficiencies of such devices diminishes as the required divergence is reduced (i.e., the quality of such devices' outputs becomes worse as their design constraints are made more restrictive).
European Patent No. EP 0354605 B1 discloses a Soller slit X-ray collimator made from a ceramic material containing heavy elements, e.g., a ceramic of lead titanate with a lead content over 60%. The production of the Soller slit described therein requires expensive ceramic materials processing, and is therefore less desirable for commercial applications.
Accordingly, it is desirable to produce blades of a Soller slit from a material that provides adequate absorption of diverging X-rays, without the problems associated with prior devices, such as those made from heavy metals. Specifically, it is desirable to provide a Soller slit device that utilizes materials that are resistant to bending, as is the case with traditional metal blades. To this end, it is desirable to provide a Soller slit that makes use of relatively low density materials. Additionally, it is desirable to produce a Soller slit device having blades with a thinner profile than conventionally used metal blades or metal foil blades, to provide a better transmission efficiency for the device. It is desirable to provide such an increase in transmission efficiency, while maintaining a low divergence angle. Additionally, it is desirable to provide a Soller slit X-ray collimator that provides the above objectives, while being relatively inexpensive to produce, to ensure that commercial advantages are maintained.
Furthermore, it is desirable to provide an X-ray diffractometer, or diffractometry system, utilizing a Soller slit comprising the above-mentioned low density materials. Specifically, it is desirable to provide a system for performing high energy radiation diffractometry, which makes use of increased transmission efficiency and low divergence angle of such a Soller slit.